1. Field Of The Invention
The present invention relates to apparatus for the removal or filtration of contaminants such as toxic gases, vapors, molecules, particles, dust and unpleasant smelling substances generated in air contained within a particular structure or working chamber and more particularly to a new and improved apparatus which provides for the optimization of the filtration or removal of such contaminants including improved safety of operation by a self-contained system without ducting.
2. Description Of Prior Art
It is well known to filter contaminated air by passing the contaminated air through a filter by a fan in order to filter out gases generated in the working chamber of a laboratory fume hood and to exhaust the filtered air back into the room where the users are present. Such prior art hood apparatus provides advantages in that they avoid the construction of costly exhaust ducts, the contamination or pollution of the atmosphere, and the consuming, by ducting to the outside, of cooled or heated air provided in the room where the hood apparatus is operated.
While such ductless prior art devices have provided improvements in certain areas there still exists numerous disadvantages.
For example, the prior art ductless fume hoods are limited in their use when the contaminants to be removed are toxic gaseous molecules. It is well known that in accordance with the inter-molecular attraction forces of the Van der Waals phenomena, when a filter such as, for example, an activated carbon filter or molecular sieve, is saturated by the accumulation of toxic molecules, the excess toxic molecules pass through the filter uninhibited. The prior art devices do not provide for any indication of the moment when filters become saturated and thereafter permit toxic contaminants to pass through the filter thereby creating a safety hazard. Even if it is assumed that a detector is used for the detection of the toxic molecules which have passed through the saturated filter, the user may be in a position where he still has to carry on with the work (which generates the toxic molecules) until completed. This could result in recirculating intolerable quantities of toxic air into the air of the room where the user is present.
Additionally, present detectors of contaminants have the disadvantage of reacting only in the presence of certain gas contaminants and in some cases only at a level of concentration which is intolerable for the users. Therefore their use is limited to the detectable gas contaminants, the threshold detection level of which is lower than the tolerable or safe threshold level of toxicity.
It is also known that the punctual (non-permanent) detectors of toxic gases, such as, for example, the common color reacting sampling test tubes are inexpensive and easy to use. They provide detection for a wide range of toxic compounds of different families but they cannot be used for the ductless filtering fume hoods due to the fact that their capacity for the detection of the saturation of the filters is of a single use for a very short period of time consisting of a few minutes, by sampling of the air exhausted by the hood.
In other words, a system of punctual detection, such as, for example, the color reacting sampling test tubes, have the advantage of an ideal scope of detection for various toxic gases and vapors and of a good accuracy in the reading of the concentrations of the sampled toxic compounds, but they unfortunately have the disadvantage to force the user to do continual repeated air samplings (at least once a day) in order to cyclically evaluate the quality of the filtration, which renders this system difficult to use for ductless filtering fume hoods.
Furthermore, it is well known that the ductless filtering and air recirculating fume hoods can ensure a proper filtration only within the limits of a quantity of toxic compounds equal to the remaining retention or saturation capacity of the filter. Therefore, if by accident after a spillage or a leak of toxic compounds, the quantity released within the working chamber was to exceed the remaining retention capacity of the filter, this would lead to discharge of toxic molecules into the room where laboratory technicians are. This disadvantage renders safety practically impossible in the case of an accident. In fact, if such an accident was to happen when the filter is at the extreme limit of its working life, it would not withstand any further overloading of toxic molecules and would not ensure a proper filtration.
The present state of the art is exemplified in the following U.S. Pat. Nos.:
______________________________________ 4,678,489 4,563,943 4,666,478 4,690,042 4,163,650 4,268,282 ______________________________________
Accordingly, a principle desirable object of the present invention is to overcome the disadvantages of the prior art.
Another desirable object of the present invention is to provide an apparatus for removing or filtering contaminants generated in a volume of air contained in a work structure and which optimizes the effectiveness of contaminant filters.
Another desirable object of the present invention is to provide an apparatus of the foregoing objects which is constructed and arranged to employ common detectors of contaminants such as toxic gases efficiently and safely.
Another desirable object of the present invention is to provide a new and improved ductless portable fume hood having revolving, removable and interchangeable filter cartridges.
These and other desirable objects of the invention will in part appear hereinafter and will in part become apparent after consideration of the specification with reference to the accompanying drawings and the claims.